Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art, exhaust a complex mixture of air pollutants. These air pollutants may include solid material known as particulate matter or soot. Due to increased awareness of the environment, exhaust emission standards have become more stringent and the amount of particulate matter emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine.
One method implemented by engine manufacturers for complying with the regulation of particulate matter exhausted to the environment has been to remove the particulate matter from the exhaust flow of an engine using a device called a particulate trap. A particulate trap is a filter, typically consisting of a wire mesh or ceramic honeycomb medium, which is designed to trap particulate matter. Unfortunately, the use of the particulate trap for extended periods of time may cause the particulate matter to build up in the medium, thereby reducing the functionality of the filter and subsequent performance of the engine.
Built-up particulate matter may be removed from the filter through a process called regeneration. To initiate regeneration of the filter, the temperature of the particulate matter captured within the filter must be elevated to a combustion threshold, at which the particulate matter may slowly burn away. Often, the temperature of the exhaust flow as emitted by the engine raises the particulate temperature to that sufficient for regeneration. During some situations however, such as low engine load or during the winter months, the temperature of the exhaust may be insufficient to raise the particulate matter to the required combustion threshold.
One way to remedy this problem is to artificially reduce the combustion threshold of the collected particulate matter to a temperature below that of the exhaust such that regeneration can be achieved. An example of a system that implements this method is described in U.S. Pat. No. 6,397,584 (the '584 patent) issued to Salvat et al. on Jun. 4, 2002. Specifically, the '584 patent discloses a system for assisting the regeneration of a particle filter integrated into an exhaust line of a motor vehicle diesel engine. This system includes a supply of additive, which is continuously injected into a fuel tank of the engine. The additive mixes with the fuel, and the mixture is combusted to produce a flow of exhaust containing soot particles bonded with a metal compound. The compound-bonded particle has a lower ignition temperature than non-bonded particles. When the lowered ignition temperature is attained with the engine's exhaust flow, the soot particles and metal compounds are burned, leaving behind ash, which may be effectively removed from the filter during periodic maintenance of the engine.
Although the system of the '584 patent may suitably regenerate a particulate filter, it may be costly and problematic. In particular, the low-temperature situations requiring the injection of the additive may be intermittent and, because the system of the '584 patent always injects that additive, some additive may be wasted. This wasted additive drives up the cost of the system. In addition, because the additive is converted to ash during the regeneration process, excessive amounts of additive may result in excessive amounts of ash. Because the maintenance interval of the engine may be at least partially based on the accumulation rate of ash within the particle filter, the excessive amounts of ash may significantly reduce the maintenance interval. A reduced maintenance interval, in addition to creating an inconvenience for the vehicle owner, also serves to increase the operating cost of the vehicle.
The system of the present disclosure solves one or more of the problems set forth above.